Air flow interlock switch



Jan. 3,- 1950 H. P. THOMAS 2,493,603

AIR FLOW inmznocx swrrcn Filed July 29, 1947 cam-Roz.

36 EQUIPMENT Za -i In ve n t or Henry F Thomas,

b w mm l-|is Attorney.

Patented Jan. 3, 1950 2,493,603 AIR FLOW YINTERLOCK swrrcn Henry P. Thomas, Fayetteville, N. Y... aasignor to General Electric Company, a corporation pf New York Application July 29, 1947, Serial No. 764,365

2 Claims. (CL 200-113) My invention relates to a fluid flow protective device for a cooling system and particularly to a protective system for forced cooled vacuum tubes.

In a high powered radio transmitter, power amplifier, or the like, it is necessary to employ some method of forced cooling, otherwise the heat dissipated by the tube elements is not carried away and the temperature rises rapidly to such an extent that it damages the tubes. In cooling systems, such as the conventional forced air system, it is necessary to have some type of protection in case of a failure of the system to provide a proper amount of coolant. Various systems have'heretofore been used, such as a centrifugal switch mounted on a blower motor shaft or a pressure operated device. These do not furnish adequate protection and cannot be relied upon invariably toshut oif the power supply to the tubes in case of a failure in the operation of the cooling system. For example, in a system employing a centrifugal switch, slippage of the belt to the blower might causea reduction in the amount of coolant, yet the switch would still remain closed. Also it requires fine mechanical adjustment and has moving parts that are subject to wear. As another illustration, in a system employing a pressure operated device, it is possible to still have adequate pressure but due to stoppage of the duct, have an insufficient volume of air. Also for quiet operation, low pressures are necessary. This requires precise mechanical adjustment, and a slight misadjustment will either cause a failure to operate or will operate needlessly causing unwanted shut downs.

It is an object of my invention to provide a positive action fluid flow protective device.

Another object of my invention is to provide a protective device that will prevent application of power in case of a failure of the device.

A further object of my invention is to provide positive protection for forced cooled tubes in case of a failure in the cooling system.

The features of my invention, which I believe to be novel, are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages, can best be understood by reference to the following drawing in which the single figure thereof represents, in vertical cross-section an air duct structure in which is installed a protective device embodying my invention. The power supply and control circuits for the protective device are shown schematically for simplicity.

Referring to the drawing, I have shown a vertical cross-section view of a flow control device i installed in conjunction with an air duct 2 of which only a fragmentary vertical cross-section is illustrated. The flow of air is represented by the arrows 3. The direction of flow is shown for illustration only as it could be in either direction. The air may be supplied from any conventional source such as a blower (not shown) but this source, and also the remainder of the duct system, have been omitted from the drawing for simplicity, since these details form no part of the present invention.

The device I comprises a perforated housing 4, having a flanged base 5, extending into the duct 2 through an opening 6. Extending axially of the housing 4 is a resistance wire 1, which has a substantial temperature coefficient of expansion. One end is attached to a supporting member 8 by solder 9 or other suitable means. The other end is attached by suitable means to an actuating contact arm II], which is formed of a unitary flat strip of spring material. The tension of the wire 1 is adjusted by means of a screw ll which extends into and engages a threaded portion of the member 8. A locking screw I2 securely anchors the member 8 in place after adjustment.

On the outer end of the contact arm [0 is mounted a contact member [3 disposed in space relation for engaging a like contact member l4 mounted on a contact arm I5 similar to the contact arm Ill but having an opening l6 therein through which the wire 1 passes. The two contact arms, l0 and I5, and a terminal member I! are stacked alternately with insulating strips it as shown, and are secured to the flange 5 by means of a metallic plate l9 and screws 20. Suitable openings in the contact arms l0 and i5 serve to insulate them from the screws 20. The screws 20 are threaded into the flange 5 so that the pressure exerted by the plate I9 upon the stack securely clamps the parts Ill, 15, I1 and ill in a fixed position. The flange 5 is attached to and insulated from a base 2| by means of insulating washers 22 and screws 23. The base 2| is secured to the duct 2 by mounting screws 24. A suitable cover 25 is mounted on the base 2| by Posts 26 and screws 21.

A source of power, represented conventionally as a battery 28, is provided for energizing the protective device. The upper terminal of battery 28 is connected to the terminal member ll through a switch 36 and conductor The terminal member I7 is electrically connected through the plate is, screws 20, flange 5 and housing 4 to the upper end of the resistance wire nected through a variable resistance 33 and'a conductor 3| to the actuating contact arm- II and to the lower end of the resistance wire 1.

With the arm III in the position shown in the drawing, contact member l3 engages contact member l4, completing a circuit for energizing the operating coil of a relay 33. This circuit may be traced from the upper terminal of battery 23, through switch .38, condugtor 29, the coil of relay 33, a conductor 32, contact arm l5, contacts l3 and I, contact arm l0, conductor 3i and resistance 30 to the lower terminal of battery 23. When relay 33 is thus'energized it maintains its contacts 34 closed so as to complete a circuit to control equipment (not shown in the drawing). This control equipment may control the energization of any apparatus whose safe operation is dependent upon the continued supply of adequate coolant through the duct 2. For example, it may control the anode power supply for high power, air-cooler tubes of a radio transmitter whose safe operation depends on continuously supplying an adequate volume of cooling air through duct 2.

' With the foregoing detailed description of the structure and arrangement of my control system in mind, its mode of operation will be clear from the following description. Assume that no coolant is flowing through duct 2 and that switch 36 is open. The tension of the wire I is now adjusted by means of the screw l I so that the actuating contact arm II! is deflected until the contact l3 engages the contact I4. Switch 36 is then closed, causing current from the battery 28 to flow through the wire I. This heats the wire I, causing it to expand, and the spring arm l tends to draw contact i3 down out of engagement with contact II. A flow of coolant may also be started, the volume of flow being adjusted for satisfactory operation of the controlled apparatus. This flow of coolant tends to carry away heat from wire I and thereby to maintain contacts i3 and I4 in engagement. The magnitude of the current through wire I is now adjusted by adjusting the variable resistance 30 so that the circuit is maintained closed unless the flow of coolant drops below a desired minimum value. So long as the contacts remain closed, relay 33 remains energized through the circuit previously traced.

When the correct adjustment is made, a. stoppage of air flow, or reduction below a safe minimum value, permits wire I to expand sufflciently for actuating arm ID to move downward and break the contact between the points l3 and I4. This in turn breaks the circuit to the relay 33 causing the contact 34 to open the equipment control circuit 35. Upon the normal flow of air being restored, the wire I cools and contracts. thereby closing the circuit and energizing the relay 33 which recloses the control circuit 35.

By making the housing 4 out of material having a temperature coefilcient of expansion similar to that of the wire 1, they will react similarly to the ambient temperature and hence tend to remain in adjustment. This will not affect the operation in case of a failure of the air supply as the heat will be concentrated in the wire.

By using a fairly fine wire, in the order of five to eight mils diameter, the speed of action of this interlock can be made fairly rapid, in the order of one second or less, thus preventing the application of power to the vacuum tubes or other protected apparatus for a long enough time after failureoi'theair coolingsystemto 'serious damagetothe equipment.

cause any One advantage of my invention is that the only I moving part is the actuating arm II. The contests are normally closed and remain so until an air failure occurs. The contacts do not operate when the switch it is opened, as the current is removed from the wire. This means that since contact is 'always maintained, except when a failure occurs, dust particles and the like cannot get on the contact surfaces and prevent good electrical contact and as the unit never operates until a failure, there are no moving parts to wear.

A further advantage is that ii the wire should break, the actuating contact arm would open the contacts deenergizing relay 33 just as for a coolant failure. In other words, the system fails safe," 1. e., the device cannot fail and permit the control circuit 35 to remain energized.

For puropses of illustration, I have shown the power supply for heating the wire I as a battery. However, it may be from any other suitable source such as the power supply for the equipment which it controls. The advantage being connected to such power supply or else interlocked with such a supply, would be that a failure of power supply for the protective device would also be a failure of the power supply to operate the equipment. Hence. it would be a safe" failure.

While I have illustrated and described a particular embodiment of my invention, modifications thereof will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not to be limited to the particular arrangement disclosed, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an air flow responsive system, an air duct, a supporting member having a relatively high coeflicient of expansion interposed in said duct, said member being secured to a wall of said duct and having a free end within said duct, a resistance wire having substantially the same high coefficient of expansion, one end of said wire being securely fastened to said free end of said supporting member, a switch member biased toward a normally open position, the other end of said wire being fastened to said switch member and normally holding said switch closed, .said wire extending alongside said supporting member, the effect of expansion of said wire due to changes in air temperature being substantially compensated by corresponding expansion of said supporting member, means for heating said wire, by a current flowing therein, to a predetermined temperature at which said wire expands in the absence of air flow in said duct sufficiently to cause said switch device to move to said open position, said switch remaining closed so long as 3 predetermined flow of air is maintained in said 2. In a fluid flow responsive system, a duct providing a coolant flow path, a transverse supporting member having a high coeflicient of expansion interposed in said path, said member being secured to a wall of said duct and having a free end within said duct, a straight resistance wire having substantially the same high coefficient of expansion, one end of said wire being secured to said free end, a switch biased to a normally open position, the other end of said wire being fastened to said switch member and pansion being sufllcient to cause said switch to 10 return to said normally open position, and means to adjust said heating current so that a coolant flow exceeding a predetermined minimum value cools said wire sumciently to cause said wire to maintain said switch closed.

HENRY P. THOMAS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,741,601 Appelberg Dec. 31, 1929 2,300,418 Hall Nov. 3, 1942 2,306,509 Talmey Dec. 29, 1942 2,344,946 Landon Mar. 28, 1944 

